From -6443465715257071186 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,c503251d87cf889e X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 1994-09-27 11:13:17 PST Newsgroups: comp.std.c++ Path: bga.com!news.sprintlink.net!howland.reston.ans.net!EU.net!sunic!news.funet.fi!news.lut.fi!hilja.it.lut.fi!hevi From: hevi@hilja.it.lut.fi (Petri Heinil{) Subject: Re: size of a "empty" class Sender: news@lut.fi (Usenet News) Message-ID: Date: Tue, 27 Sep 1994 18:06:49 GMT References: Nntp-Posting-Host: hilja.it.lut.fi Organization: Lappeenranta University of Technology, Finland Lines: 43 In article , g2devi@cdf.toronto.edu (Robert N. Deviasse) writes: > In article , Tom O Breton wrote: > > ... > >Your class is not empty. It has a hidden pointer to a virtual table. > >Frankly, I don't think you understand what you are talking about here, > > > Just because you can't currently see how something can be otherwise does not > mean that it can't be so. Yes, for an example: I want to do some image prosessing in OO way, I have type-class Pixel, there is needed the 8 bit for 256 state gray scale. And the protocol is defined something like show, calculate, etc. to the manager object. And when I do for example edge detection, I need two classes inherited from Pixel: a EdgePixel, that has a 8 states for the direction where the egde goes and has different behaviour for show (the line) or calculation, and the other class is NormalPixel that has standard pixel behaviour. The EdgePixel are commonly minor number in calculated image. And how I want get the edges from the 2048 x 2048 image, so if there exist in compiler tagged optimization for virtual functions the size likely needed is 2048 * 2048 * 8 / 8 = 4 Mbytes and if the are virtual pointer with the Pixel the size needed is 2048 * 2048 * (8 + 40) / 8 = 20 Mbytes that can't happen in normal machine (today) with 16 Mbytes ram. The other question is does the compiler optimization rules belongs to the standard definition, because they are partially implementation issues. Alhough the C++ now posess the optimization directives like "register" or "volatile", derived from the ANSI C. And the C++ is low level language (it have pointers), so the optimization might be appropriate. -- -- The Page --